1. Field of the Invention
The present invention relates to an expandable/contractible intermediate shaft used in a steering apparatus of, e.g., an automobile, in which an entire length thereof diminishes in the event of a collision accident, thereby preventing a steering wheel from thrusting a driver's body up.
2. Related Background Art
It has hitherto been widely practiced that an expandable/contractible intermediate shaft is provided midway of a steering apparatus in order to prevent a steering wheel from thrusting a driver's body up in the event of a collision accident. This expandable/contractible intermediate shaft diminishes an entire length if a front portion of the automobile is crashed subsequent to a so-called primary impact in which the automobile collides with other automobile. Such an expandable/contractible intermediate shaft is constructed by making a serration or spline engagement between one end of an outer tube member and one end of a solid inner shaft member. Further, as disclosed in Japanese Utility Model Post-Exam Publication No. 63-17862, there has hitherto been known a structure for causing no backlash in the engaging portions between one end of the outer tube member and one end of the inner shaft member.
FIG. 29 shows an expandable/contractible intermediate shaft disclosed in this publication. An inner peripheral surface of an outer tube member P1 is formed with a female spline P2, and an outer peripheral surface of a solid inner shaft member P3 is formed with a male spline P4 engaging with the female spline P2. Further, slits P5, P5 each opening at one edge of the outer tube member P1 are formed in a plurality of positions in a circumferential direction of one end of the outer tube member P1. Moreover, a ring-like fastening member P6 is externally fitted to one end of the outer tube member P1. This ring-like fastening member P6 elastically fastens an inner peripheral surface of one end of the outer tube member P1 onto the outer peripheral surface of the solid inner shaft member in a state where the inner shaft member P3 is inserted into the outer tube member P1. Then, a backlash in engaging portions between the female and male splines P2, P4 is thereby prevented irrespective of a minute gap existing between the female spline P2 and the male spline P4.
The conventional structure shown in FIG. 29 is capable of preventing the backlash in the engaging portions between the female and male splines P2, P4. An operation of preventing the inner shaft member P3 from disengaging from the outer tube member P1 before assembling the expandable/contractible intermediate shaft to the steering apparatus, is, however, incomplete. Hence, there might be a possibility that the inner shaft member P3 disengages from the outer tube member P1 when a worker holds and lifts only one of the inner shaft member P3 and the outer tube member P1 by a hand and so on in the course of being carried from a manufacturing factory of the expandable/contractible intermediate shaft to an automobile assembly factory or during an assembling operation in the assembly factory.
In the case of being used as an intermediate shaft constituting the steering apparatus of the automobile, first and second universal joints of a joint cross type for connecting a steering shaft or an input shaft of a steering gear, are attached to portions at both ends. Phases of the pair of first and second universal joints enable the intermediate shaft fitted with these two universal joints to be installed in a limited space, or offset non-constant velocities possessed by the individual joint cross type universal joints. Therefore, the assembly is performed in the manufacturing factory of the expandable/contractible intermediate shaft in a state of giving a predetermined phase difference in the rotating direction. Accordingly, after the inner shaft member P3 has disengaged once from the outer tube member P1, even when the worker properly inserts the inner shaft member P3 into the outer tube member P1, the intermediate shaft can not be fitted, and, even if could be fitted, there must be a deviation in relationship between an operating angle of the steering wheel and a steering angle given to a front wheel, with the result that the non-constant velocity becomes conspicuous.
An expandable/contractible intermediate shaft of the present invention is invented, for the purpose of obviating the problems described above, to actualize a structure in which the inner shaft member P3 never disengages from the outer tube member P1 except when required before being assembled to a steering apparatus such as when carried and when in the assembling process and so forth.
Incidentally, another problem is that, if the disengagement occurs, phases of the first universal joint connected to the inner shaft member and of the second universal joint connected to the outer tube member come to be unknown with the result that it must be time-consuming to make the phases coincident, or the torque largely fluctuates in the actual vehicle due to an out-of-phase mis-insertion.